文档介绍：Language Testing Basic principles 2017-5-16 2 ? To understand the need for test theory, it is first necessary to understand something about the fundamental nature of measurement , constructs , and psychological tests. 2017-5-16 3 What are they measuring? Height & weight ? physical attributes psychological attributes 2017-5-16 4 ? Unlike physical attributes, the psychological attributes of an individual cannot be measured directly as can height or weight. ? They are hypothetical concepts - products of the informed scientific imagination of social scientists who attempt to develop theories for explaining human behavior. ? The existence of such constructs can never be absolutely confirmed. ? The degree to which any psychological construct characterizes an individual can only be inferred from observations of his or her behavior. What is Measurement ? Measurement in the social sciences is the process of quantifying the characteristics of persons according to explicit procedures and rules . ? Quantification: assign numbers ? Characteristics: physical and mental characteristics of persons (abilities/construct) ? Procedures and rules : replicable, for other observers, in other contexts and with other individuals. 2017-5-16 6 ? A well-known classification of measurement scales is given by Stevens (1951). These measurement scales are: ? 1. the nominal scale ? On the nominal scale objects are classified according to a characteristic. ? An example: one can classify persons with respect to sex, hair color, etc. ? 2. the ordinal scale ? An ordinal prises the numbering of different levels of an attribute that are ordered with respect to each other. ? Example: individuals are ranked ‘ first ’, ‘ second ’, ‘ third ’ and so on. ? 3. the interval scale ? An interval scale is a numbering of different levels in which the distances, or intervals, between the levels are equal. ? 4. the ratio scale ? The ratio scale has a natural origin as